1. Field of the Invention
The present invention relates generally to the modification and control of the temperature of a selected body organ. More particularly, the invention relates to applications of selective organ cooling which advantageously employ complementary techniques.
2. Background Information
Organs in the human body, such as the brain, kidney and heart, are maintained at a constant temperature of approximately 37xc2x0 C. Hypothermia can be clinically defined as a core body temperature of 35xc2x0 C. or less. Hypothermia is sometimes characterized further according to its severity. A body core temperature in the range of 33xc2x0 C. to 35xc2x0 C. is described as mild hypothermia. A body temperature of 28xc2x0 C. to 32xc2x0 C. is described as moderate hypothermia. A body core temperature in the range of 24xc2x0 C. to 28xc2x0 C. is described as severe hypothermia.
Hypothermia is uniquely effective in reducing brain injury caused by a variety of neurological insults and may eventually play an important role in emergency brain resuscitation. Experimental evidence has demonstrated that cerebral cooling improves outcome after global ischemia, focal ischemia, or traumatic brain injury. For this reason, hypothermia may be induced in order to reduce the effect of certain bodily injuries to the brain as well as other organs.
Cerebral hypothermia has traditionally been accomplished through whole body cooling to create a condition of total body hypothermia in the range of 20xc2x0 C. to 30xc2x0 C. However, the use of total body hypothermia risks certain deleterious systematic vascular effects. For example, total body hypothermia may cause severe derangement of the cardiovascular system, including low cardiac output, elevated systematic resistance, and ventricular fibrillation. Other side effects include renal failure, disseminated intravascular coagulation, and electrolyte disturbances. In addition to the undesirable side effects, total body hypothermia is difficult to administer.
Catheters have been developed which are inserted into the bloodstream of the patient in order to induce total body hypothermia. For example, U.S. Pat. No. 3,425,419 to Dato describes a method and apparatus of lowering and raising the temperature of the human body. Dato induces moderate hypothermia in a patient using a metallic catheter. The metallic catheter has an inner passageway through which a fluid, such as water, can be circulated. The catheter is inserted through the femoral vein and then through the inferior vena cava as far as the right atrium and the superior vena cava. The Dato catheter has an elongated cylindrical shape and is constructed from stainless steel. By way of example, Dato suggests the use of a catheter approximately 70 cm in length and approximately 6 mm in diameter. However, use of the Dato device implicates the negative effects of total body hypothermia described above.
Due to the problems associated with total body hypothermia, attempts have been made to provide more selective cooling. For example, cooling helmets or head gear have been used in an attempt to cool only the head rather than the patient""s entire body. However, such methods rely on conductive heat transfer through the skull and into the brain. One drawback of using conductive heat transfer is that the process of reducing the temperature of the brain is prolonged. Also, it is difficult to precisely control the temperature of the brain when using conduction due to the temperature gradient that must be established externally in order to sufficiently lower the internal temperature. In addition, when using conduction to cool the brain, the face of the patient is also subjected to severe hypothermia, increasing discomfort and the likelihood of negative side effects. It is known that profound cooling of the face can cause similar cardiovascular side effects as total body cooling. From a practical standpoint, such devices are cumbersome and may make continued treatment of the patient difficult or impossible.
Selected organ hypothermia has been accomplished using extracorporeal perfusion, as detailed by Arthur E. Schwartz, M.D. et al., in Isolated Cerebral Hypothermia by Single Carotid Artery Perfusion of Extracorporeally Cooled Blood in Baboons, which appeared in Vol. 39, No. 3, NEUROSURGERY 577 (September, 1996). In this study, blood was continually withdrawn from baboons through the femoral artery. The blood was cooled by a water bath and then infused through a common carotid artery with its external branches occluded. Using this method, normal heart rhythm, systemic arterial blood pressure and arterial blood gas values were maintained during the hypothermia. This study showed that the brain could be selectively cooled to temperatures of 20xc2x0 C. without reducing the temperature of the entire body. However, external circulation of blood is not a practical approach for treating humans because the risk of infection, need for anticoagulation, and risk of bleeding is too great. Further, this method requires cannulation of two vessels making it more cumbersome to perform particularly in emergency settings. Even more, percutaneous cannulation of the carotid artery is difficult and potentially fatal due to the associated arterial wall trauma. Finally, this method would be ineffective to cool other organs, such as the kidneys, because the feeding arteries cannot be directly cannulated percutaneously.
Selective organ hypothermia has also been attempted by perfusion of a cold solution such as saline or perflourocarbons. This process is commonly used to protect the heart during heart surgery and is referred to as cardioplegia. Perfusion of a cold solution has a number of drawbacks, including a limited time of administration due to excessive volume accumulation, cost, and inconvenience of maintaining the perfusate and lack of effectiveness due to the temperature dilution from the blood. Temperature dilution by the blood is a particular problem in high blood flow organs such as the brain.
The invention provides a practical method and apparatus which modifies and controls the temperature of a selected organ and which may be used in combination with many complementary therapeutic techniques.
In one aspect, the invention is directed to a method for selectively controlling the temperature of a selected organ of a patient for performance of a specified application. The method includes introducing a guide catheter into a blood vessel and providing a supply tube having a heat transfer element attached to a distal end thereof. The heat transfer element has a plurality of exterior surface irregularities, the surface irregularities having a depth greater than the boundary layer thickness of flow in the feeding artery of the selected organ. The supply tube and heat transfer element are inserted through the guide catheter to place the heat transfer element in the feeding artery of the selected organ. Turbulence is created around the surface irregularities at a distance from the heat transfer element greater than the boundary layer thickness of flow in the feeding artery, thereby creating turbulence throughout the blood flow in the feeding artery. A working fluid is circulated into the heat transfer element via the supply tube. The working fluid is circulated out of the heat transfer element via the guide catheter. Heat is thereby transferred between the heat transfer element and the blood in the feeding artery to selectively control the temperature of the selected organ.
Implementations of the invention may include one or more of the following. The surface irregularities on the heat transfer element may include a plurality of segments of helical ridges and grooves having alternating directions of helical rotation. Turbulence may be created by establishing repetitively alternating directions of helical blood flow with the alternating helical rotations of the ridges and grooves, and may be induced for greater than 20% of the period of the cardiac cycle within the carotid artery.
In another aspect, the invention relates to a method for selective thrombolysis by selective vessel hypothermia. The method includes introducing a guide catheter into a thrombosed blood vessel, delivering a thrombolytic drug to the blood by flowing the thrombolytic drug into the guide catheter, and introducing a supply tube having a heat transfer element at a distal end thereof into the thrombosed blood vessel through the guide catheter. The heat transfer element is cooled by flowing a working fluid through the heat transfer element, the return path for the working fluid being the guide catheter. The blood is thereby cooled to a prespecified temperature by flowing the blood past the heat transfer element. The system may also be used to heat the blood for hyperthermia applications.
Implementations of the invention may include one or more of the following. The drug may be chosen from the group consisting of tPA, urokinase, streptokinase, precursors of urokinase, and combinations thereof. For hypothermia applications, if the thrombolytic drug is streptokinase, the prespecified temperature range may be between about 30xc2x0 C. and 32xc2x0 C. If the thrombolytic drug is urokinase or a precursor to urokinase, the prespecified temperature range may be below about 28xc2x0 C. For hyperthermia applications, if the thrombolytic drug is tPA, the prespecified temperature range may be between about 37xc2x0 C. to 40xc2x0 C.
In another aspect, the invention is directed to a selective organ heat transfer device and guide catheter assembly. The assembly includes a guide catheter capable of insertion to a selected feeding artery in the vascular system of a patient, the guide catheter having a soft tip and an interior retaining flange at a distal end. The assembly also includes a flexible supply tube capable of insertion in the guide catheter and a heat transfer element attached to a distal end of the supply tube. The heat transfer element has a flange at a distal end, the flange capable of engagement with the retaining flange to prevent the heat transfer element from disengaging with the guide catheter. A plurality of exterior surface irregularities are disposed on the heat transfer element, the surface irregularities being shaped and arranged to create turbulence in surrounding fluid, the surface irregularities having a depth at least equal to the boundary layer thickness of flow in the feeding artery.
Implementations of the invention include one or more of the following. A strut may be coupled to the supply tube at a distal end thereof. The heat transfer element may include a plurality of heat transfer segments, and may further include a flexible joint connecting each of the heat transfer segments to adjacent the heat transfer segments. The flexible joint may be a bellows, a metal tube, a plastic tube, a rubber tube, a latex rubber tube, etc.
In another aspect, the invention is directed to a method for performing angiography during selective vessel hypothermia. The method includes introducing a guide catheter into a blood vessel and delivering a radioopaque fluid to the blood by flowing the radioopaque fluid into the guide catheter. A supply tube having a heat transfer element at a distal end thereof is introduced into the blood vessel through the guide catheter. The heat transfer element is cooled by flowing a working fluid through the heat transfer element, the return path for the working fluid being the guide catheter. Blood is thereby cooled by flowing past the heat transfer element. Thus, the cooling can occur at or near the same time as angiography.
In another aspect, the invention is directed to a method for performing stenting of a stenotic lesion during selective vessel hypothermia. The method includes introducing a guide catheter into a blood vessel and introducing a guide wire through the guide catheter and across a stenotic lesion. A balloon catheter loaded with a stent is then delivered via the guide wire such that the stent is positioned across the lesion. The balloon is expanded with contrast, after which the stent may be deployed. The heat transfer element and supply tube may then be employed to cool the blood as described above. Similarly, the cooling can occur at or near the same time as the stenting procedure.
In another aspect of the invention, a return catheter may be coupled to a heat transfer element, distal end of the heat transfer element defining a hole. The return catheter and heat transfer element may together form a xe2x80x9cguide catheterxe2x80x9d through which may be placed a guide wire, a microcatheter, etc. In particular, a catheter may be placed therein having a tapered shape such that the catheter lodges into the hole. The catheter may have an outlet at a distal end to allow drug delivery, an outlet upstream of the distal end to allow delivery of a working fluid to the interior of the heat transfer element, or in some cases both.
Advantages of the invention include the following. The device may be placed in an artery without traumatizing the arterial wall and with damaging the device itself. The device may be placed in an artery simply and by a variety of practitioners such as cardiologists or neurosurgeons. The device allows the complementary performance of simultaneous procedures along with brain cooling, these procedures including angiography, stenotic lesion stenting, and drug delivery.
The novel features of this invention, as well as the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and in which: